Conversion of kraft lignin under hydrothermal conditions

• Hydrothermal treatment of kraft lignin.
• Maximum value of total oil yield (11% of kraft lignin).
• Main compounds of oils.
• Guaiacol amount (78% of oil) at 130 °C/60 min.
• Conversion mechanism is reported using GPC and FTIR.

The aim of this study is to explore hydrothermal conversion of kraft lignin for value-added products. With ranging between 5.4% and 10.6%, total oil yield decreased with the increase of temperature (130, 180, and 230 °C), the longer reaction time (15–60 min) led to increased total oil yield. Main compound of oils characterized by GC–MS was guaiacol (2-methoxy phenol) in the range of 19–78% of oil depending on different reaction conditions. Residual kraft lignins were characterized by GPC and FTIR with respect to the conversion mechanism of kraft lignin by this process. The conversion of kraft lignin under hydrothermal conditions had something to do with the degradation of β-O-4 linkages, hydroxyl groups, carbonyl groups, aromatic rings resulting in the increased amount of phenolic OH groups in kraft lignin.